Flowing gas streams often contain particulate material that must be removed from the stream. The particulate material may be an undesirable contaminant in the gas stream. Alternatively, the gas stream may contain a desirable particulate material, for example, in a process for manufacturing the particulate. Similarly, flowing gas streams may contain liquids, either desirable or undesirable, that must be removed from the gas stream.
There presently exist several systems and methods for removing particulate material and/or liquids from gas streams, including inertial, viscous, diffusion, and electrostatic separation systems and methods. Further background regarding available systems and methods may be found in the applicant's Technical Paper Fundamentals of Gas Solids/Liquids Separation, Gas Machinery Research Council, Dallas, Tex. (2004), hereby incorporated by reference, and in the applicant's publication, Principles of Air Filtration, available at <http:www.muellerenvironmental.com>.
An example of an application that requires the removal of liquid and particulate from a flowing gas stream occurs in the transmission of natural gas. Natural gas is often introduced into and transmitted through a pipeline system with entrained liquids and particulate. Additional particulate often enters the natural gas pipeline as a result of cleaning the pipeline, for example, during periodic inspection of the pipeline wall thickness. This cleaning and inspection has recently become more important with federal regulations that mandate more frequent inspections. Cleaning the interior of a natural gas pipeline removes debris from the pipeline wall, which then enters the natural gas stream. The particulate and liquid must be removed before the gas stream enters the gas compressors, where it could otherwise damage or degrade the efficiency of the compressors.
Other applications that require the removal of liquids and particulate from flowing gas streams include the filtering of the inlet gas flow entering gas turbines or reciprocating engine-drive compressors, separating sand from water (e.g., separating produced water from “frac” sand in oil and gas wells), and removing large volumes of liquids that have been used to plug or “kill” natural gas wells.
Traditional filter separators used in these and other applications, for example, two-stage filter and vane separators, are generally capable of removing only 10% by weight of liquid before the liquids begin to pass through the filter separator and into the compressor or other machinery. Centrifugal compressors may pass through these liquids within a gas stream, but reciprocating compressors may be seriously damaged by the presence of even small amounts of liquid. Furthermore, changing or cleaning the filter elements in these traditional systems is often complex and labor-intensive. Often, the flowing gas stream must be stopped or rerouted to bypass the separation device or other machinery. Then, the internal system pressure must be reduced to atmospheric pressure. Personnel using hazardous material safeguards then enter the system, manually replace filters clogged with large quantities or very viscous materials, and manually clean the interior spaces of the filter separator. After cleaning, the filter separator must then be closed, the bypass removed, and the system re-pressurized or brought back online. During the entire cleaning process, machinery connected to these systems is typically shut down. Further, the material thus removed from the system may also be considered hazardous and require special precautions for disposal.
Accordingly, there exists a need for new systems and methods for removing particulate and liquids from flowing gas streams wherein the new systems and methods are capable of effective operation at varying gas flow rates and potentially high liquid-to-gas weight ratios. Preferably, such systems should also provide easier maintenance, require less frequent cleaning, maintain operational status during cleaning, and produce less potentially hazardous waste products.